This invention relates to an actuating mechanism for simultaneously adjusting the optical powers of two variable focal length lens units which form part of a pair of spectacles. The invention is described in connection with lens units of the type disclosed in U.S. Pat. Nos. 5,138,494 (FIG. 9), 5,371,629, and 5,688,620. The disclosures of all of said patents are relevant hereto and are accordingly included herein by reference.
For purposes of convenience in explaining the present invention, a lens unit embodiment is shown herein which is comprised of 1) a front ring assembly which includes a distensible membrane stretched across the field of view of the lens unit, 2) a rear ring assembly which includes a rigid lens across the field of view of the lens unit, 3) a transparent liquid filling the space between the front and rear ring assemblies, 4) a sealing bellows which keeps the liquid from escaping, yet allows relative motion between the front and rear ring assemblies, and 5) hinging means between the front and rear ring assemblies. As the front and rear ring assemblies of a lens unit are moved closer and further apart (by rotation about the hinging means) the focal length of the lens unit is decreased or increased (i.e., its optical power is increased or decreased). More discussion of the construction and operation of such lens units may be had by reference to the aforementioned patents.
When two lens units are assembled into a pair of spectacles, it is necessary that an actuation means be provided to control the spacings of the ring assemblies simultaneously in such a way that changes in optical power of the lens units track closely. The present invention is intended to provide such a means. The normal tolerance for the optical power of lenses used in ophthalmic spectacles is .+-.1/8 diopter, hence it is desirable that the two variable focus lens units in a pair of spectacles track within that tolerance.
It is accordingly an object of the present invention to provide an actuation mechanism for variable focus spectacles that simultaneously adjusts the optical powers of the two embedded lens units in such a way as to minimize any tracking differences.